This invention pertains to electrodes and, in particular, to electrodes for use with molten carbonate fuel cells.
In the design of electrodes for molten carbonate fuel cells, it is essential that the electrodes be provided with carbonate constituent to provide the needed bridge with the carbonate electrolyte tile. In present structures, one technique for providing the needed carbonate constituent is to fill the electrolyte tile with excess carbonate and allow some of the excess to drain into the electrodes. The electrolyte becomes depleted in the tile and electrodes during the course of fuel cell operation and limits the useful life of the fuel cell.
A storage of excess carbonate electrolyte can be provided in the electrolyte tile by increasing its thickness. However, increasing the tile thickness decreases the fuel cell output and, thus, is undesirable.
To avoid having to increase the tile thickness, other practices have been used in which carbonate electrolyte is supplied directly to the electrodes. While this requires increased electrode thickness, such increased thickness is not detrimental to cell performance. Present techniques for adding carbonate electrolyte to the electrodes, however, are inefficient and could have an adverse effect on the electrode characteristics.
In particular, carbonate electrolyte is usually added by melting the electrolyte directly into the electrode at high temperatures (e.g., 600.degree. C.). When this is carried out using gases that the fuel electrode would normally be subjected to during fuel cell operation, wetting of the electrode is poor and inhibits electrolyte absorption. Thus, in this case, the high temperatures used can adversely affect the electrode characteristics and the degree of added electrolyte is not substantial. Moreover, while the amount of electrolyte can be increased by using a different gas during the heating, the change in gas composition can also adversely affect the electrode characteristics.
It is therefore an object of the present invention to provide a practice for incorporating carbonate electrolyte into an electrode which does not suffer from the above disadvantages.
It is a further object of the present invention to provide an improved electrode for molten carbonate fuel cells.